Line a 9- x 5-inch loafpan with plastic wrap, extending edges of wrap over sides of pan; set aside.
Combine 1/2 cup whipping cream, chocolate squares, corn syrup, and butter in a heavy saucepan; cook, stirring constantly, over low heat until chocolate melts. Cool.
Beat remaining 1 1/2 cups whipping cream, powdered sugar, and vanilla at high speed with an electric mixer until stiff peaks form; fold into chocolate mixture. Pour into prepared pan, and chill at least 8 hours.
Process raspberries in a blender or food processor until smooth, stopping once to scrape down sides. Pour purée through a fine wire-mesh strainer, if desired, pressing with the back of a spoon; discard seeds. Chill.
Invert mousse loaf onto a serving platter, and remove plastic wrap. Slice loaf, and serve with raspberry puree. Garnish, if desired.